Packet switched networks route voice traffic using a Voice Over Internet Protocol (VoIP). VoIP allows telephone calls to be carried over an Internet Protocol (IP) network between two telephones or computers.
Authorization systems verify user authorization to particular phone services before allowing the phone network to connect the call. The authorization system usually exchanges certain parameters between a Network Access Server (NAS) that receives inputs from a user and an authorization server that has access to a user database containing authorization information for valid users.
Credit based authorization is one type of authorization based phone call. With credit based authorization, the user sets up a debit account with a telephone company prior to making phone calls. The debit account often takes the form of a preapproved calling card. When the user wishes to make a phone call, the authorization system verifies that the user has sufficient credit on the calling card account before connecting the phone call. As the call continues, the authorization system continuously tracks the cost of additional time of the call and subtracts the additional cost from the remaining credit in the calling card account. The authorization system notifies the user when the credit limit is about to run out on the calling card. If the user continues to talk past the remaining credit limit, the authorization system terminates the phone call.
In VoIP networks, a call is established through the packet switched network via a local gateway. A central authorization server in another part of the network tracks state information regarding the authorization based call. State information includes account identification information associated with the call, the rate for the current call, the elapsed time of the current call, the amount of credit remaining on the prepaid calling card, etc.
The authorization server keeps state information for all open authorization based calls that go through the same authorization system. This centralized authorization system does not scale well. This is because all open authorization based calls are managed by the same authorization server. There is also a reliability (robustness) problem with a centralized authorization server. If the authorization server crashes, all open authorization based calls could be disconnected. State information for all the open authorization based calls can also be lost when the authorization server crashes, creating accounting errors.
Another problem exists with tracking authorization based call states from a central authorization server. The gateways that establish the call connections between two different endpoints are typically not prepared to respond to signals sent asynchronously from the authorization server. Thus, if the authorization server identifies a call exceeding a user's credit authorization, the gateway may not be able to disconnect the call in a timely manner.
Thus, the need remains for improving the scalability and reliability of authorization based telephone systems.